Yeah, A circuit would be refurring to wires. You may have a wire loose or a ground thats not grounding good. As to were it is, I do not really know. You will have to start looking around the fuel pump and go along those wires looking for cuts or something of that nature.

Okay, here ya go. This is straight from a web forum for professional technicians called iATN. It is a subscription-only site.

P1237=Fuel Pump Secondary Circuit (Fuel Pump Driver Module)

Electronic Returnless Fuel Systems (ERFS) utilize a Fuel Pump Driver Module (FPDM) to control fuel pressure. The PCM uses a Fuel Rail Pressure Sensor (FRP) for feedback. The PCM outputs a duty cycle to the FPDM to maintain the desired fuel rail pressure. During normal operation, the PCM will output a FP duty cycle from 5% to 51%. The FPDM will run the fuel pump at twice this duty cycle, e.g. if the PCM outputs a 42% duty cycle, the FPDM will run the fuel pump at 84%. If the PCM outputs a 75% duty cycle, the FPDM will turn off the fuel pump.

If the FPDM does not out any diagnostic signal, (0 or 100% duty cycle), the PCM sets a P1233 DTC. This DTC is set if the FPDM loses power. This can also occur if the Inertia Fuel Switch is tripped.

If the FPDM outputs a 25% duty cycle, it means that the fuel pump control duty cycle is out of range. This may occurs if the FPDM does not receive a valid control duty cycle signal from the PCM. The FPDM will default to 100% duty cycle on the fuel pump control output. The PCM sets a P1235 DTC.

If the FPDM outputs a 75% duty cycle, it means that the FPDM has detected an open or short on the fuel pump control circuit. The PCM sets a P1237 DTC.

I have this code on my 1999 Mystique 2.5l build date 7/99. I replace the fuel pump and now even with the key in the on position, the pump runs forever. I will state a guy a work, jump the two ground wires at the connector (to the fuel pump) together. Could this be causing the CEL? Thanks!

Register Now

In order to be able to post messages on the Ford Focus Forum, Ford Focus ST Forum, Ford Focus RS Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:

Password

Please enter a password for your user account. Note that passwords are case-sensitive.

Password:

Confirm Password:

Email Address

Please enter a valid email address for yourself.

Email Address:

What I Drive

Year, color, and model of your car. Example: 2003 Pitch Black ZX3

Name

Your real name.

City

State

Country

Insurance

Please select your insurance company (Optional)

Log-in

User Name

Remember Me?

Password

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.